It is customary to obtain samples of particulate material periodically from a moving belt to determine whether or not the particulate material meets specifications agreed upon by the supplier. Particulate materials may take a variety of forms such as ore, wheat, grain, coal, slurries, fertilizer, etc. While the invention set forth in this application has specific application to the sampling of coal in electric utilities, it is to be understood that the invention is not to be so limited, but has application to particulate material in any size range and when mixed with a liquid.
In the past, samples have been obtained by the free fall method wherein the particulate materials are carried on a moving belt to a point where the particulate material drops off the belt down to another moving belt and a bucket-shaped sample collector or moving diversion chute traverses the falling stream and collects the samples.
The major disadvantages of this system are the amount of headroom (from 7 to 20 feet) that is required and the cost of supporting structures and extra conveyors that are necessary.
As a consequence, in recent years the hammer or swing sampler has been gaining a certain amount of popularity. This sampler may be attached to any existing moving conveyor belt and rotates at right angles to the belt and periodically sweeps off a sample of particulate material into a chute for sampling.
The disadvantages of this device are that the effective opening of the sample cutter is limited because while it is also moving at right angles to the belt, the belt, of course, is also moving and, as a consequence, a diagonal path is cut through the particulate material on the belt resulting in a snowplowing action in front of the sample collector and a damming action on the upstream side of the sample collector as it moves across the belt. The use of the term "upstream" herein means the location from which the particulate material is moving on the belt. The term "downstream" means the location to which the particulate material is being taken. Thus the effective opening of this type of sample collector is significantly reduced and the constituents being sampled that are acquired by the sample cutter tend not to be in exactly the same proportions that they exist in the material being sampled. When a sample cutter going through the particulate material disturbs it, the probability is increased that the variable constituents will not be present in the sample in exactly the same proportions that they are on the belt. Such a sample collector will tend to selectively reject by particle size or shape various pieces of particulate material so that the variable constituents will be obtained in different proportions than they exist in the total mass being sampled.